1. Field of the Invention
This invention relates to assembling a tube in a tubesheet of a heat exchanger, and more particularly, to guiding the tube through spatially separated tube support and tubesheet apertures and radially expanding the tube into contact with the wall of the receiving tubesheet aperture.
2. Description of the Prior Art
Tube installation through tube support plates and tubesheets of shell and tube heat exchangers has traditionally been accomplished by physically pushing a tube in a first direction through generally aligned apertures in spatially separated tube supports and at least one tubesheet. Tube-to-tubesheet aperture misalignment being compensated for by transversely redirecting the tube's leading end and guiding it through the misaligned aperture(s). Tapered tube guides insertable in the tube's leading end have often been used to facilitate tube pushing by substantially reducing the manual intervention of transversely redirecting the tube's leading end to attain suitable tube-to-tube aperture alignment along the length of the tube. Such tapered tube guides are well known in the art and have, heretofore, been removed from the leading tube end prior to connecting the tube to the tubesheet. The connection process was normally a radial enlargement of the tube, often accomplished with a rolling tool inserted in the open end of the tube and radially expanded therein. An alternative and sometimes more reliable tube-to-tubesheet connection constitutes welding the two together. Prior to such welding, however, a preliminary or "tack" roll has usually been used to temporarily secure the tube in the desired configuration with the tubesheet to ensure the accuracy of a subsequent weldment therebetween.
Utilizing separate processes of tube guide extraction and subsequent tube expansion, although time consuming, was not believed to present a major disadvantage to installing tubes in conventional shell and tube heat exchangers. However, in the case of nuclear steam generators or other shell and tube heat exchangers whose primary or channel head side has been exposed to a hazardous environment such as radioactivity, it is desirable to expedite tube repair or replacement operation within the channel head so as to minimize the workmen's exposure time to the hazardous environment.
Automated tube guide extraction and tube expansion substantially eliminate exposure of workmen to the channel head's hazardous environment. An apparatus for extracting tube guides from tubes frictionally engaged therewith is described in commonly assigned allowed application Ser. No. 898,348, filed Apr. 21, 1978. An apparatus for hydraulically expanding the tubes following guide removal is illustrated in commonly assigned U.S. Pat. No. 4,125,937, filed June 28, 1977. The separate extraction and expansion apparatus were designed to be driven by and mate with a support-positioning device operable within a steam generator's channel head. Such support-positioning device (hereinafter referred to as an R.theta. machine) is described in commonly assigned allowed application Ser. No. 888,701, filed Mar. 21, 1978.
When straight tubes are utilized in a heat exchanger, a single R.theta. machine can be assembled on the primary side of the tubesheet within the channel head, but when U-tubes are utilized such as is common practice in nuclear steam generators, a separate R.theta. machine is preferably installed on both sides of the channel head's separating plate which isolates primary fluid entering the channel head from the fluid after it has traversed the tubes and is exiting the channel head. Use of multiple R.theta. machines ensures initial tube guide extraction and tube end expansion of the lesser protruding tube end through the tubesheet. Initial guide extraction from and expansion of the greater protruding tube leg can cause retraction of the shorter protruding tube leg toward the secondary side of the tubesheet. Subsequent guide extraction and expansion of the retracted tube leg necessitates "pulling" the tube leg toward the primary side into proper configuration with the tubesheet. "Pushing" rather than "pulling" the tube leg into proper relative position with the tubesheet was judged easier and more desirable. Protrusion differences between the U-tube legs is inherent due to accumulation of manufacturing and assembly tolerances. Since it is not predictable which leg of the U-tube will protrude further through the tubesheet, two R.theta. machines are necessary to efficiently extract the guide and expand the tubes.
Such R.theta. machines, when used with the aforementioned copending application's tube guides, extraction apparatus therefor, and tube expander, provide automated, remote extraction of the tube guides and expansion of the tubes as well as minimizing workmen exposure to the radioactive environment of the nuclear steam generators' channel heads. However, since separate apparatus or tools are needed to extract the tube guides from the tubes and then expand those tubes, a tool change on both R.theta. machines is called for. Such tool change is most efficiently performed by workmen within the hostile environment of the channel head. It would be desirable to further minimize workmen exposure to the channel head's radioactive environment and increase the speed with which the tube guide extraction and tube expansion is accomplished.